A substrate processing apparatus configured to hydrophobize a substrate by supplying a HMDS (hexamethyldisilazane) gas onto a surface of the substrate placed in a processing vessel is described in Patent Document 1.
Patent Document 1: Japanese Patent Laid-open Publication No. 2013-004804
In a processing in which a preset gas is supplied to a substrate as a processing target, like the aforementioned hydrophobic processing, it may be difficult to detect a state of the gas within an apparatus.